Title

Author

Date of Award

2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

R.D. LeFever

Abstract

The Frobisher-Alida interval consists of eight log-defined subintervals or “beds” within the Mississippian upper Mission Canyon and lower Charles Formations of the Madison Group in the Williston Basin. The subintervals are composed of predominantly evaporite and carbonate lithologies, and include in descending order: 1) Midale, 2) Rival, 3) Bluell, 4) Sherwood, 5) Mohall, 6) Glenburn, 7) Wayne, and 8) Landa. The top of the lower six subintervals are separated by thin but areal extensive log-defined markers of contrasting lithologies and include in descending order: 1) State A, 2) Sherwood Argillaceous Marker (S.A.M.), 3) K-1, 4) K-2, 5) K-3, and 6) Landa Marker. An additional localized marker, State A2, is identified defining the lower boundary of an Upper Bluell subinterval. This study focuses on the lithologic and sequence stratigraphic significance of markers with the exception of the Landa Marker.

The area studied covers Burke, Mountrail, Renville, Ward, western Bottineau and northwestern McHenry Counties in North Dakota. Geologically, the region is situated on the eastern flank of the Williston Basin; characterized by a shallow dipping (between 0.25 and 0.5 degrees) carbonate platform of an epicontinental sea on the western flank of the North American craton.

Seventy-three marker descriptions were completed on the six markers from fifty-eight different cores throughout the study area. Six lithotypes reflecting unique depositional conditions were identified within the markers and include: 1) anhydrite, 2) dolomudstone, 3) dolomitic sandstone, 4) calc-mud/wackestone, 5) grain-supported, and 6) skeletal wackestone. Of these, the dolomudstone and dolomitic sandstone lithotypes are considered characteristic marker bed lithotypes, while the remaining are present as interbeds. The lithotypes reflect deposition in a variety of environments from a supralittoral, salina-like embayment to the east, through shallow sublittoral settings and into an open marine environment to the west.

The section studied lies within the first-order Kaskaskian megasequence and second-order Madison sequence which includes part of the upper Bakken shale and extends to the basinwide Madison unconformity. The Frobisher-Alida interval represents a single third-order sequence spanning 2-3 million years and the compositional subintervals are considered fourth-order sequences.

The subintervals are progradational and become increasingly restrictive up section and therefore represent individual fourth-order regressive systems tracts. Markers dominated by the dolomudstone lithotype (State A, State A2, S.A.M.) reflect deposition during a highstand systems tract where the basal contact represents a fourth-order maximum flooding surface. Dolomitic sandstone markers reflect initial deposition during a lowstand systems tract with unconsolidated sediments reworked and further cemented with the subsequent transgressive tract. Contrasting sediment input and consolidating mechanisms obscure definitive sequence surfaces; therefore, a sequence stratigraphic model is defined that places the maximum regressive surface at the lower contact and maximum flooding surface at the upper contact of the sandstone dominated markers.